Apparatus for treating hydrocarbon vapors



W. F. SIMS ETAL APPARATUS FOR TREATING HYDROCARBON VAPORS Sept. l, 1931.

ations,

Sept. l, 1931. w. F. sims ET AL APPARATUS FOR TREATING HYDROCARBON VAPORS Filed May 7, 1929 2 ASheets-shew 2 Patented Sept. 1, 1931 PATENT oFFlcE WILLIS F. SIMS AND VENUS U. CLOER, 0F WICHITA FALLS, TEXAS, ASSIGNORS T0 PANHANDLE REFINING COMPANY, OF WICHITA FALLS, TEXAS, A CORPORATION or TEXAS APPARATUS FOR TREATING HYDROCAIRBON VAPORS Application filed May 7, 1829.

Our invention relates to the treat-ment of hydrocarbon oils and especially to such treatment for the purpose of producing motor fuel from petroleum by the process commonly known as cracking. The present application is a continuation in part of our prior copending application filed February 16, 1928, Serial No. 254,753, in which we have described and claimed an improved method of cracking under vacuum and a complete plant for practicing the same. In the presentI case we shall describe the same general system, together with improved primary and cracking stills combined in one structural unit, and shall claim said unit construction, as well as certain specific features and methods of operation of the plant as a Whole.

Very briefly stated, the invention we present has for its basis the .discovery on our part that by cracking, fractionating, and cooling under a vacuum, in whole or in part, we can increase the yield of a product containing unsaturated compounds and aromatr -ics which is eminently suitable for motor fuel; and that by suitably regulating the temperatures and pressures (sub-atmospheric) in different parts of the system, we can not only greatly econolnize heat and thereby economize fuel, but we can also produce a product containing practically 100% of the desired unsaturates and aromatic compounds.

Our apparatus, -as it will be described, comprises a preheating still for the charging stock, a cracking still, preferably preceded by a tiashpot into which the oil from the preheater is expanded into vapors, and a succession of interrelated fractionating towers or dephlegmators with one or more vacuum pumps, heat exchanger, and cooler and separator, an absorption tower, all arranged as will be described in detail hereinafter. In addition `to the regulation of pressures in each element of the system, from the preheater to the separator and absorber, we have found it possible to arrange a graduated heat transfer by means of which lnake-upoil, or retluxed fractions to be cracked, take up practically all t-he heat Serial No. 361,015.

energy in the cracked vapors, in a counter current progression through the fractionators. The make-up oil and refluxed fractions instead of going direct to the cracking still, have their temperature raised so that they can be converted into vapors in the flashpot, flom which the vapors pass, together with those from the primary heater, to the cracking still.

By maintaining a vacuum or a sub-atmos pheric pressure in the cracking zone (and preferably in the flashpot and fractionators), cracking commences at a lower temperature, while the raising of the absolute temperature, together with the turbulent and rapid motion of the vapors through the cracking tubes due to the pull of the vacuum, causes a considerable increase in the amount of heat energy taken up per square foot of surface, with a corresponding increase in the amount of cracked products. lVitliout limiting ourselvesl to one specific set of pressures, we have found in actual practice that suitable pressures for our system and our method are from 0 to 60 pounds on the primary heating still, from l2 to 14 pounds absolute pressure on the flashpot, and from 6 to 14' pounds absolute (or a higher vacuum) on our cracking zone, fractionating towers, cooler and separator. It is to be understood thatthe word vacuum as used in Ithis specification means therefore any pressure below that of the atmosphere, but the actualpressures employed will be stated in pounds absolute.

' A particular feature which we shall claim herein both broadly and specifically, is the arrangement of the unit struct-ure containing the preheating still and the cracking tubes. Ve preferably arrange this with twin furnaces connected by an arched overhead opening, with burners in both furnaces. The heat passing upward in the cracking furnace then follows a down draft through the preheat-ing furnace, which has upper and lower flue passages into the stack, containing dampers by means of which the heat supplied to the preheater tubes may be regulated.

The details of construction will sufficiently l the preheater and cracking still taken on the line 2 2 of Fig. 3.

Fig. 3 is a horizontal longitudinal section of the same, taken on the line 3-3 of Fig. 2.

Referring to the drawings, and first to Fig. 1, 1 designates a flashpot adapted to receive the heated oil through valve 23 and pipe 52 from the pipe still in the. furnace 2.a.. Charging stock is forced into said pipe still through the pipe 53 by pump 54. The oil may enter the flashpot as vapors already formed, or it maybe superheated oil up to the point of its entrance into the fiashpot and transformed to vapor in this pot by release from or reduction of pressure. The vapors from this flashpot passing through pipe 55 to the cracking tubes 56 1n .the furnace 2, will be ator above the equilibrium boiling point of the oils from which the are produced. This equilibrium boiling point is referred to the temperature of the vapors under such pressures as that carried on our flashpot. This is a vapor temperature and not an oil temperature. The oil before entering the flashpot 1 in order to be converted completely into a vapor therein, must be at a temperature somewhat above this vapor temperature in order to contain enough heat to take care of the latent heat of vapor1za tion of the oil on entering the flashpot.

The preheating of the oil before it enters the flashpot is accomplished in an improved still of our design, one form of which is shown in Fig. 1 and another form in Figs. 2 and 3. In Fig. 1, the pipe still 57 is located in the furnace chamber 2a which is preferably supplied with top and bottom flue openings 5859 into the stack 60, each opening being provided with a damper as shown, so that the draft through the pipe 57 may be regulated. The furnace cham ber 2a is provided with burners 61, which are manipulated in a manner presently to be described and the entire structure of the furnace and the pipe still is connected to the structure of the furnace 2 containing the cracking tubes 56, and main burner 62. The two chambers 2 and 2a.]are connected in this case by means of one or more openings 63 so that the heated gases and products of combustion from the burners 62, after passing through and around the cracking tubes 56, will be drawn through the passages 63 and then enter the stack 60 through either the lower or upper opening 59 or 58, according to the adjustment of the dampers or equivalent devices. With the upper draft of 58 open, all the waste heat from the cracking furnace 2 passes through and aroundthe preheating tubes 57, and the oil therein is'thus raised to a temperature suitable for flashing and introduction as vapors into the cracking tubes 56.

The burners 61 placed under the primary heating tubes are used in bringing the plant on stream at the beginning of a run. By using these burners 61 we do not have to fire the cracking tubes 56 (by means of burner 62) so heavily as would otherwise be the case and the temperature of the oil in the primary tubes is quickly raised to such a point that vapor is formed when released to the flashpot 1. After the plant is once on stream and the maximum fire is placed under the cracking tubes 2 by burners 62, the burners 61 may be turned down very low or completely cut out and the temperature of the oil flowing in the primary heater may thereafter be regulated byAv the proper use of the dampers as already stated. lVe believe this method of and apparatus for preheating and cracking the oil is original with us and we shall claim the same accordingly.

Referring to Figs. 2 and 3, we have therein shown a modified form of preheater and cracking still in one unit structure, which we prefer to use in practice. derstood that the form shown in Fig. 1 is somewhat simplified as -forming a part of the diagram in that figure, while Figs. 2 and 3 show an actual working structure. In these figures. the enclosure 2a is built on the side of the main furnace 2, and they are. connected b v an arched roof The cracking tubes 56 and the preheating tubes 57 are disposed horizontally and parallel to each other in the two chambers 2 and 2a, with their bends lying outside the end fire walls of the respective chambers, and enclosed with thin metal plates 65-66-67-68. The furnace 2 is lengthened out at both ends as shown in 2m and 2y, these two ends being arched as indicated in dotted lines 21e in Fig. 2, and constituting dutch ovens pro- ]ecting into which are the burners 62. Burners 61 project into the furnace 2a bcneath the prelieating tubes 57 and all the burners in practice are fitted with appropriate valves. In operation the heated gases and products of combustion from the bilrners 62 are received in the dutch ovens .2.17 and 2y, and conveyed through the arches 21e into the central chamber 2, passing upwardlv therein through and around the cracking tubes 56 and thence being deflected bv the arch 2 through the passageway 63a' into the chamber 2n. If the burners 61 are in operation at the same time, 'for purposes of bringing the plant on stream, then 'the damper in the upper flue 59 should be open and that in the lower flue 5S should be closed.

It will be un- After the plant is on stream as already stated, and the maximum fire is placed under the cracking tubes 56, then burners 61 may beturned down very low or completely eilt out, and by regulating the dampers in flue passages 58-59, more or less of the heated gases coming through the passageway 63a may be deflecteddownwardly through and around the/preheating tubes 57, and into the stack 60 through the lower flue passage 58. Therpreheater and cracking still thus combined in one unit have certain definite advantages in point of accessibility, as well as the primary advanzone 2 pumping the vapors so removed from' tages ofveiiciency and economy.

The Vaporsfrom flashpot 1 are drawn through the cracking tubes 56 preferably at a temperature from 10000 F. to 12000 F., and as already stated a pressure of 6 to 14 pounds absolute is maintained on the cracking tubes by vacuum pump 14. This low pressure on the vapors causes the temperature at which the cracking reaction takes place to be lowered. It also causes the velocity of the vapors, considering a constant gallonage of raw oil charged, to be higher than 'in a system operated at or above vatmospheric pressure, and this vapor velocity gives a more turbulent flow'of the vvapors in the tubes causing a greater heat transfer pel' square foot of heating surface.l The vacuurn pump 14 is located in such a position with suitable connections,.lines 30, 39,

40, and '42, and valves 3, 4, 5, 19, 46, 20,' 21' and 25, that the vacuum may be applied at the discharge from the tubes in the heating the tubes to cooling and separation tower 6,

or the vacuum may be applied on the sep-r arator drum 10 and the vapors so removed` discharged into absorption tower 11.

The vapors entering the cooling and separation tower 6 may be at or below atmospheric pressure, depending on the point `at which the vacuum is applied to the system, and will be at an elevated temperature, preferably from 10000 F. to 1200o F., depending on the temperature found most suitable for treatment of the vapors being passed through the system to 4give the largest practical yield Lof gasoline or related light oils,

siderable-quantities of heat that must be removed before the products of the react-ion produced in the tubes can-'be condensed andf' made to be stable under atmospheric conditions. This heat is removed in. two waysv through valve 18 to tower 6,'preferably contacted with the hot vapors over a series of battle plates placed in this tower, and (2) Because of this elevated tem--v perature of these vapors they contain conby causing fthe vapors to come in contact pors is caused to lowby pump 15. This causes the heat to be removed by (l) vaporizing the incoming oil from tower 7, and (2) by the absorption of the heat by the cooler oil flowing in the cooling coils. This cooling eli'ect will cause a heavy residue to collect inthe bottom of the cooling` and separation tower 6 which is removed from the system by pump 12, as presently described.

The vapors from cooling and separating tower 6 enter the cooling and separation tower 7, at or below atmospheric pressure depending on the point at which vacuum is placed on the system and in tower 7 they `are further cooled and fractionated. This tower is preferably of the bubble type. The cooling is .effected by causing the vapors to come into contact with cooling coils 27 and 27, placed in this tower, through whichV oil .of relatively lower temperature than the vapors entering the tower is caused to 'low by'pump 15. The cooling in this tower is carried to such a p`oint that a large portion of the vapors entering it are caused to condense to liquid. This liquid is drawn from tower ration tower 8 at or below atmospheric pressure depending on the point at which the vacuum is `applied to the system, and in .tower 8 they are further cooled and fractionated; This cooling and separation tower is'preferably of the bubble type.. Cooling is effected by causing the vapors to come in Valves 18 and contact with the coil 28 through which. oil

at a lower temperature than the vapors is caused to flow by pump 15. This cooling allows a considerable portion of the vaporsv to be condensed and the condensed fractions are removed from the bottom of the tower through the heat lexchanger 17 bythe pump 15. A part of theoil, after having been cooled by passing through the heat exchanger 17, is discharged by pump 15 through valve 31 into the absorption tower 11, and a part of the oil is discharged through` coils,28 and 27, 27 through valve 32. Valves'31 and 32 may be soopened or closed as to cause a Vdesired quantity to flow in either direction, or all or any part of the How to go` in either direction.

The vapors in the cooling and separating tower 8 are also cooled by the liquid from the bottom of the absorption tower 11 which is pumped from tower 11 by pump 16 through heat exchanger 17 where the temperature of this liquid is raised by liquid iowing in a counter current from the bottom of tower 8, and it is then discharged into tower 8 through valve 33. The temperature of the liquid entering tower 8 may be conytrolled by by-passing the heat exchanger with a portion of the cold liquid from absorber 11. This by-pass may be of any suitable or desired construction, and is shown at in the drawings.` The liquid from absorber 11 contains the very light fractions not condensed by water cooling coil 9. These absorbed light fractions are removed from this liquid on its entrance'into tower 8fdue to the heat it gains in heat exchanger 17 and the hot vapors entering tower 8.

The vapors from the cooling and separa tion tower 8 are caused to ass through water cooling coils 9 where t ey are condensed at atmospheric pressure or lower depending on the point at `which the vacuum is' applied to the system. vThis condensate, because of the coolmg and separation it has previously had, is gasoline or related light oils and is collected in separator drum 10. This light liquid is removed from the separator drum 10 through valve 29 by a pump not shown in the drawings.

. The vapors that collect in separating drum 10 are either drawn from it by vacuum pump 14 or are caused to pass into absorbing tower 1l by reason of their own pressure. This depends on the point at which the vacuum is being applied to the system. These vapors -llow in a counter-current to the cooled liquid from the bottom of the cooling and separating tower 8 and the ,y lighter gasoline or related lighter oils are absorbed in this liquid. The tower 11 is preferably of the bubble type.

The xed gases pass from the tower 11 f through line 47 to the atmosphere, or are conducted to burners under the furnace, or

vare conducted to commercial gas lines.

The bottoms from tower 8, either with or l without make-up oil, delivered through line them. yThe heated liquid from coils 26, 26',r

and valve 35, not required as absorption 011 in the tower 11, are returned to the system and used as cooling oil in coils 28, 27,

' 27', 26, 26, 26', which are placed in towers 8, 7 and'6. The line conducting this oil to cooling coils 28, 27 and 27 has valves 36 and 37 so situated that all or any part of this liquid can be caused to flow through n Q26 and 26" is conducted through line 22 and through valve 38 to flash pot 1 where s all or a considerable-portion of this oil is lvaporized. The vapor so produced is retreated in the furnace 2 by being drawn through the tubes placed in this furnace.

It is to be understoodthat .the above ap,- paratus is only one of the forms of apparatus that may be used to obtain light oils from hydrocarbon vapors by our process. The form of apparatus is governed largely by the nature of the vapor under treatment.

The apparatus described above when operated an vapors from petroleum gas oil of approximately B. gravity with a vacuum capable of holding .up a 5-inch column of mercury maintained on the system at the separation drum valve 29, gave a yield of 16 to 60 percent'of light oils having a new Navy gasoline boiling range and 3 to 5 percent of absorbed light oils whichwhen separated resembled natural gasoline in its boiling range. This gasoline is high in unsaturates and aromatics containing from to percent unsaturated compounds and from 10 to 25 percent of aromatic compounds, and is a very desirable motor fuel.

Having thus described in general the operation of our system, it may be remarked that by varying the combinations of valves, pumps, direct and reflux feed, it is possible to use the same apparatus in-various ways and for different operations, with different classes of oils. The type of equipment used in our process will, of course, also vary with the kind of vapors under treatment. The equipment shown in our drawings is that used when operating on vapors produced from 28 to 36 gravity gas oil derived from petroleum. The apparatus as shown is designed to crack'the vapors in the most eiiicient way, and then remove the heat from the cracked vapors in such a manner that the heat so removed will not be lost but taken up by oil that is to be vaporized and returned to the cracking zone. In this case the heat is removed in four successive stages, in such a manner as to cause the vapors to condense forming into four different products, one of these products being the finished gasoline or related light oil--the desired.

A product for which the plant was designedlargely as a heat exchanger between the incomlng vapors from the cracking tubes in the furnace 2 and the oil being charged into the system, from which lva ors are tobe produced. The vapors which enter this tower are at a relatively high temperature, that temperature being from 1000o F to 1200 F. In this tower the surface of the y asphaltic material coils 26, 26, 26, 26 containing the charging oil should be such as to transfer enough of the heat contained in the vapors to the charging oil so that the vapors leaving this tower will be at from 720o to 650 F. At this temperature there will be a very heavy removed from these vapors which if allowed to remain in the tower 6 would eventually harden and plug the tower due to the heat of the incoming vapors.' 'To keep this from happening we provide valve 18 through which a quantity of the heavy gas oil from the bottom of #7 tower may be introduced into tower 6. This heavy gas oil dissolves the asphaltic material removed from the vapors in tower 6 and carries it to the bottom of the tower Where it is drawn off by pump l2 as a liquid residue suitable for fuel oil. The heavy gas oil introduced into this tower also serves as an added cooling medium for the incoming vapors and gives us a more flexible control over the temperature of the gases ,leaving the tower. This tower 6 contains at its top the heat exchanger shown in the drawings as coils 26, 26', 26 and 26 and in the bottom it contains baille pans over which the heavy gas oil being' introduced into the tower is made to flow to keep it washed free of the heavy asphalt-like' material. Of course it is not necessary that this tower contain baille pansonly as shown, for anything placed in the tower which willl contact the gases with the heavy gas oil and at the same time cause it to How around in the tower to dissolve all asphalt-'like material will do equally as well, as an equivalent of the baille pans.

The temperature of the vapors entering tower 7 should be approximately at the equilibrium boiling point of thesevapors under the conditions maintainedl in that tower. vAt this temperature the quanti'tyof heat to be removed from these vapors is only that heat dueto the condensation of the heavy gas oil we desire to remove in tower 7 and the heat we must extract `from the vapors themselves in orderto 4cool the vapors to such a temperaturethat the heavy gas oil will liquefy and drop out of the vapors The heat to be relnoved in this tower is not so great in quantity as that removed in tower 6, therefore the heatexchanger at the top of this tower, which has a surface only suilcient to transfer the heat from the vapors to the -the condensing-heavy gas oil. In order to thoroughly strip this heavy gas oil of these heavy gas oil before it is withdrawn from the tower by pump 13. Even an open column below this condenser would suffice if made long enough. However, we have chosen to use and illustrate bubble pans because we can thereby cut down the length of the tower and also cut down the heat of radiation, thereby lessening the heat losses of the system.

Tower 8 operates on the same eneral principles as does tower 7, except or the fact that it is used to remove the light gasoline absorbed from vapors entering tower 11. In this tower enough heat is taken from the vapors entering it to cause the condensation of a light gas oil and to cool the vapors to where they are made up of only fixed gases and the desired gasoline like vapors. As the quantity of heat removed in this tower is less than the heat to be removed in the preceding towers, we have shown the heat exchanger .at the-top of this tower with only one coil, 28. Below this coil we have bubble pans 51 ,which serve to strip the condensed light gas oil of its absorbed gasoline and also to stripv the absorbing oil from tower 11 of its light gasoline by contacting them preferablyin counter-current with the incoming vapors. As in they other tower we Ycould get the same effect without bubble pans but they are given preference here for reasons already stated.

The vapors from tower 8 pass to water cooler 9 where they are brought to atmospheric temperature under which condition the gasoline like material is all condensed except for that entrained 1n the fixed gases. This condensed liquid and fixed gases are separated in drum 10, the gasollne like material going to storage or any'other place desired and the fixed gases passing to tower 11 wherethey are stripped of their entrained light gasoline by flowing Vcounter current to a down flow of light gas oil removed from the bottom of tower 8 or other light gas oil introduced from an outside source through valve 35.

The light gas oil from the bottom of tower 8 is drawn through heat exchanger 17 by pump 15 Where it loses its heat to cold 'oil drawn from the bottom of tower 11..

This exchange of heat here cools the light gas oil from tower Sto suchan extent that it can be used in tower 11 to such a degree that when it is introduced again into tower 8 very little added heat from vapors entering tower 8 is necessary for the complete removal of the light gasoline this oil has absorbed while passing through tower 1l. By this system of stripping the absorbing oil of its light gasoline content in the presence of the heavier gasoline vapors, we get a product more stable under atmospheric conditions than is gasoline produced in the ordinary way and having the light strippings from the absorbing oil added to it afterwards. In other words, the absorbing tower 11 operating in connection with the tower 8, constitutes a stabilizing system which also takes advantage of the heat available in bottoms from tower 8, and uses the same to strip the absorbing oil of its light gasoline content.

What we claim is:

l. Apparatus for the treatment of hydrocarbon oils comprising in combination an initial heater adapted to retain pressure, an expansion chamber or lashpot, means for releasing initially heated oils from said heater into said expansion chamber or flashpot, a still having an open connection tov said lashpot adapted to receive the oils therefrom and means to heat the oils in the vapor phase in said still to cracking temperature, cooling and separating means connected to receive the cracked vapors, and suction means connected so as to create and maintain a constant vacuum or subatmospheric pressure on the oil vapors insaid cracking still and through its open connection with the iashpot on the content of said flashpot, together with means to receive condensed oils from the cooling and separating means, and means to pass the same back under pressure to the Hashpot for retreatment, without passing through the initial heater.

2. Apparatus for the treatment of hydrocarbon oils comprising in combination an initial heater adapted to retain pressure, an expansion chamber or flashpot, means for releasing initially heated oils from said heater into said expansion chamber or flash-- pot, a still having an open connection to said ashpot adapted to receive theoils `therefrom and means to heat the oils in the vapor phase in said still to cracking temperature, cooling and separating means connected to receive the cracked vapors, and suction -means connected so as to create and maintain a constant vacuum or subatmospheric pressure on thejoil vapors in said cracking still and through its open connection with the iashpot on the content of said lashpot, together with means to receive condensed oils from said cooling and separating means, means to reheat the same to a suitable temperature for flashing into vapors again, and means to pass the same when reheated under pressure back into the flashpot.

3. Apparatus of the class described, comprising means for initially heating oil to a vaporizing temperature while maintainingV pressure thereon, a flashpot and means to release the oil therein, a cracking still connected to said flashpot and adapted to receive the oil therefrom and means to maintain a sub-atmospheric pressure thereon, means to heat the same therein to cracking temperatures, fractionating means connected to receive cracked vapors from the cracking still and to separate Vand condense heavier fractions thereof, and power driven pumping means suitably connected to receive and force condensate under pressure into and through said fractionating means in a counter direction to the incoming cracked vapors, whereby heat from said vapors is transferred to said condensate, means to conduct said condensate thus reheated to the. flashpot, and means to release the same therein.

4. Apparatus of the class described comprising a primary heater, a flashpot, a cracking still or retort, fractionating means, a cooler and separator, and oil and vacuum pumps, said fractionating means comprising a plurality of unitsconnected in tandem, the last element being connected also in tandem lwith the cooler and the separator, said vacuum pump being connected to produce a sub-atmospheric pressure on the entire system from the cooler back to said cracking sorption tower, a cooler and separator adapted to condense and separate all gasoline-like material passing over from. the last vfractionating unit, except that entrained in the fixed gases, means to convey said xed gases with entrained gasoline'into said absorption tower, and means to produce a counter current through said tower of condensate and make-up oil to absorb said gasoline, a pump acting to deliver said oil and the absorbed gasoline to a fractionating unit preceding the cooler and separator, wherein the same absorbs heat and the gasoline is thereby removed from-said oil, passes over to the cooler, andis cooled and condensed. Y 6. Apparatus for the treatment of hydrocarbon oils comprising in combination an initial heater adapted to retain pressure, an

expansion chamber or fiashpot, means for4 releasing,v initially heated oils from said heater into said flashpot, a still having an open connection to said iiashpot adapted to receive the oils therefrom, and means to heat crude material being treated, and the prodn uct desired.

7. Apparatus for the treatment of petroleum oil comprising a preheater, means for heating and means for maintaining pressure in said heater, a fiashpot with its input connected to the output of said heater, a cracking still connected to the out-put of said flashpot, a plurality of fractionators or dcphlegmators connected in tandem with their first input connected to the output of said cracking still, a cooler and separator connected to the last output of said fractionat-ors, a suction pump and a valved suction pipe extending therefrom adaptedito produce forward suction through the system and a subatmospheric pressure on said cracking still and flashpot, an oil pump wlth a feed pipe connected therefrom to the output of the last fractionator, and al pressure pipe extending therefrom through heating coils in the several fractionators to the flash!A pot. whereby suction is exerted forward through the system and pressure is maintained backward through the system on the distillate or make-up oil as it is heated until it is released into the flashpot.

In testimony whereof we hereunto aiiix our signatures.

VILLIS F. SIMS. VENUS U. CLOER. 

